Certain types of printing systems are adapted for printing images on large-scale substrates, such as museum displays, billboards, sails, bus boards, and banners. Some of these systems use so-called drop on demand ink jet printing. In these systems, a piezoelectric vibrator applies pressure to an ink reservoir of the print head to force the ink out through the nozzle orifices positioned on the underside of the print heads. A particular image is created by controlling the order at which ink is ejected from the various nozzle orifices.
In some of these systems, a carriage which holds a set of print heads scans across the width of a flexible substrate while the print heads deposit ink as the substrate moves. In another type of system, a solid, non-flexible substrate is supported on a table. The carriage holding the print heads has two degrees of motion so that it is able to move along the length as well as the width of the substrate as the print heads deposit ink onto the substrate. And in yet another arrangement, a solid, non-flexible substrate is held to a table as the entire table and substrate move together s along one axis of the substrate under the print heads as the carriage holding the print heads traverses in a direction normal to that axis while the print heads deposit ink to create a desired image.
During the printing process, as the carriage traverses along a pair of rails, the position of the carriage may vary because of the rails are not positioned to be precisely parallel to each other or within a plane. In some prior art systems, the rails are supported on a milled or machined support structure, or the rails are epoxied to a support structure. In these prior art systems, it is very difficult to readily adjust the position of the rails to within a desired tolerance. It is desirable, therefore, to adjust the position of the rails such that they are parallel to each other and are parallel relative to a common plane to within a desired tolerance.
In one aspect of the invention, a positioning system for a carriage in a printing system includes a support plate having a groove along a length of the plate, and a rail positioned along the groove. A first adjusting mechanism is used to adjust the position of the rail in a first direction, and a second adjusting mechanism is used to adjust the position of the rail in a second direction that is substantially normal to the first direction.
Embodiments of this aspect can include one or more of the following features. The groove can be shaped such that the rail makes a two-point contact with the groove along the length of the rail. The support plate has a second groove along the length of the plate located on an opposite side of the plate across the width of the plate. The first and the second groove are substantially parallel to each other. There can be a second rail positioned in the second groove. The position in the first direction can be maintained to a tolerance of about xc2x10.0005 inch, and the position in the second direction can be maintained to a tolerance of about xc2x10.0005 inch. The first and the second adjusting mechanisms can be jack-screw mechanisms.
In a related aspect, a method of positioning a carriage holding a set of print heads includes adjusting the position of a rail aligned along a groove of a support plate in a first direction with one or more first adjusting mechanisms, and adjusting the position of the rail in a second direction that is substantially normal to the first position with one or more second adjusting mechanisms.
The method can include adjusting the position of a second rail aligned along a second groove of the support plate that is substantially parallel to the first groove in the first direction with one or more of the first adjusting mechanisms. The first groove and the second groove can be located on opposite sides of the plate across the width of the plate. In some embodiments, the method includes adjusting the position of the second rail in the second direction with one or more of the second adjusting mechanisms. The adjusting mechanisms can be jack-screw mechanisms.
Among other advantages, the present invention provides a cost-effective means for an operator of the positioning system to quickly align the rails with just two sets of adjusting mechanisms. Further, the rails can be presciely positioned within a desired tolerance. Even if a support beam to which the plates are secured sags, for example, in an unsupported midsection portion of the beam, an operator can easily compensate for this sag by adjusting the position of the rails so that they remain parallel to each other and to a common plane. Further, the combination of the rails and the support plates form a stiff truss. This truss structure is stable and dampens any motion imparted on the structure thereby minimizing any motion transmitted to the carriage, hence, minimizing any undesirable carriage motion.